Reduced water oxygen levels affect maximal feed intake, but not protein or energy utilization efficiency of rainbow trout (Oncorhynchus mykiss)

This study examined the effect of reduced water oxygen levels on the utilization efficiencies of energy and protein from a diet fed to rainbow trout. An experimental diet was fed at one of the four ration levels with an additional starved treatment also included in each oxygenation regime. Oxygen levels in each oxygenation regime varied with ration level, but averaged 9.3 ± 0.36 mg L⁻¹ for the normal regime and 5.7 ± 1.4 mg L⁻¹ for the hypoxia regime. Significant differences were observed in the apparent satietal feed intake levels in each oxygenation regime, but not at any of the pair-fed restricted levels. No significant effects of oxygenation regime were observed on the utilization of either energy or protein by the fish. Efficiency of protein use varied depending on the protein intake level, but was not significantly affected by oxygenation regime. This study demonstrates that a reduction in the oxygen levels of the water does not affect the utilization efficiency of dietary digestible protein and energy in rainbow trout, but does result in a downregulation of feed intake when the fish is fed to apparent satietal levels.     

The dietary linoleic and linolenic fatty acids requirements of the prawn Penaeus monodon

The dietary requirement of the prawn Penaeus monodon for linoleic (LOA) and linolenic (LNA) fatty acids was examined in the absence of other long-chain polyunsaturated and highly unsaturated fatty acids (PUFA-20:2, 20:3, 22:2, 22:3 and HUFA-18:4, 20:4, 20:5, 22:4, 22:5, 22:6, respectively). Incremented dietary amounts of LOA (7, 14, 21, 28 and 35% of total fatty acids) and LNA (0, 7, 14, 21 and 28% of total fatty acids) were examined in a 5 × 5 factorial growth experiment lasting 50 days. An additional diet containing both PUFA and HUFA (cod-liver oil) was provided as a reference. The total lipid content (excluding sterols) of each of the 26 diets was maintained at 70 g kg⁻¹ of dry diet. The fatty acid composition of the neutral lipid was manipulated by blending different plant oils and supplementing with purified free fatty acids to provide the desired fatty acid composition upon addition to the total diet. At the end of the 50-day growth experiment, the prawn digestive gland (DG) was quantitatively analysed for lipid and fatty acid content. Prawns fed the reference diet increased in weight (mean ± SEM) by 214 ± 6%. Growth was generally greater when combinations of LOA and LNA were used. The best growth (213 ± 17%) was obtained with the diet containing a fatty acid content of 14% LOA and 21% LNA. This growth was comparable to that of the reference diet. The digestibility of the total lipid in the diet was usually higher when both fatty acids were present. The lipid content of the DG was highest in prawns fed diets containing both LOA and LNA, similar to the growth response. The fatty acid composition of the prawn's DG lipid reflected the fatty acid composition of the diet. However, the maximum assimilation of LNA in the DG lipid (14.2% of DG lipid fatty acids) was about half that of LOA (32.5% of DG lipid fatty acids).     

The nutritional management of barramundi, Lates calcarifer– a review

Barramundi nutrition research has been undertaken since the 1980s. From that time to the present, the requirements for most nutrients, energy demand, ingredient utilization and the effects of nutrition on flesh quality aspects have all been examined to varying extents. Optimal protein content of diets has been shown to vary with diet energy density and also the size of fish that are being fed. Most studies have suggested a protein requirement from 450 to 550 g kg^?1. For small fish, a protein to energy ratio of 25 to 30 g MJ^?1 is suggested. Limited work has been carried out on fish larger than 500 g. The 10 essential amino acids for other fish are also considered to be required by barramundi. Proportional requirements have been identified for methionine, lysine and arginine. Protein utilization efficiency by barramundi has been estimated at 46% efficiency. Iteratively determined protein and amino acid requirements suggest that the requirement for protein and amino acids will decrease with increasing fish size and are largely consistent with empirically determined requirements. Lipid requirements for energy and essential fatty acids (EFAs) show that smaller fish performed the best with a dietary lipid level of 140–160 g kg^?1, while growth of larger fish continued to improve with lipid levels up to 190 g kg^?1, although no higher levels were examined. EFA requirements have been identified for long‐chain n‐3 fatty acids and minimum levels of 10 g kg^?1 have been indicated. An optimal ratio of n‐3 to n‐6 fatty acids of 1.5 to 1.8:1 was also suggested. Barramundi have shown limited capacity to utilize dietary carbohydrates for energy, with starch digestibilities below 30% at even low inclusion levels. Barramundi also exhibit limited glycaemic control, being unable to rapidly reduce blood glucose levels. Requirements have been demonstrated for several key vitamins and quantitative requirements determined for varying forms of ascorbic acid (vitamin C). Quantitative requirements have also been established for pyridoxine and pantothenic acid but only qualitative assessments for other key vitamins. Few mineral requirements have been identified. Phosphorus is the only mineral to be studied and a requirement between 5.5 and 6.5 g kg^?1 is suggested. Energy demands of barramundi have been shown to be largely driven by thermodynamic demands on metabolic requirements and the demand for somatic energy deposition. Energy utilization by barramundi has been estimated as 68% efficient. Energy demands for maintenance are shown to be related to liveweight by an exponent of about 0.8. Variations in temperature are shown to vary the maintenance energy requirement but do not affect the efficiency of energy utilization. Feed management through feed specification selection has been shown to be possible through selection of feed protein and energy content based on the fish's change in somatic energy density. Typically, this leads to the use of lower protein and higher energy density feeds with larger fish. Ration allocation based on changes in fish size and temperatures has been studied from both iterative and empirical perspectives, and tables were developed based on these findings. Several key feed ingredients have been evaluated for their digestibility, palatability and energy and nutrient utilization. Among those ingredients were meat meals, lupin kernel meals, soybean meals and some plant oils. Limited effects of feed ingredients on flesh quality have been noted, although some effects of diet nutrient and energy specifications have been noted.     

A reference diet for nutritional studies of the giant tiger prawn Penaeus monodon

Critical evaluation of the nutrient requirements of an animal requires the use of a purified reference diet. In this study, the effects of either a purified reference experimental diet, a practical experimental diet and an imported commercial diet on the growth and nutritional condition of the prawn Penaeusmonodon were compared. The reference diet, based on widely available ingredients of consistent and known nutrient content, supported excellent prawn growth when fed either ad libitum or subsatiation (≈ 75% of the mean initial satiation intake). In a 6-week experiment, growth (as percentage increase in weight, ± SEM) of the prawns fed ad libitum differed significantly (P < 0.05) between each diet in the order: practical (142 ± 10%), reference (121 ± 9%) and commercial (91 ± 16%). Growth for the reference diet fed subsatiation was 116 ± 4%, and was not significantly (P > 0.05) different from that obtained with the same diet fed ad libitum. Dry matter food conversion for the reference diet was significantly (P < 0.05) better when fed subsatiation (1.58 ± 0.08) rather than ad libitum (2.08 ± 0.06) and better than that obtained with either the practical (3.40 ± 0.15) or commercial (3.02 ± 0.28) diets, which were not significantly (P > 0.05) different from each other. The lipid content (mg g^–1 of prawn) of the digestive gland of prawns fed ad libitum was similar for reference, practical and commercial diets (6.03 ± 0.38, 4.92 ± 0.90 and 4.92 ± 0.95 mg g^–1 of prawn, respectively), but significantly (P < 0.05) higher than that for the reference diet fed subsatiation (4.73 ± 0.38 mg g^–1 of prawn).     

A comparison of the growth performance of rainbow trout (Oncorhynchus mykiss) when fed soybean,narrow‐leaf or yellow lupin meals in extruded diets

This study compared the effect of increasing dietary inclusion of soybean, narrow‐leaf lupin or yellow lupin kernel meals when fed to rainbow trout. Each meal was formulated into a test diet to create a series of inclusion levels of 0, 100, 200, 300 and 400 g kg^?1. Each diet was formulated to the same digestible protein and energy specifications. The diets were fed to apparent satiety to 30.0 ± 0.71 g rainbow trout for 28 days. After this period, fish in the reference (0 g kg^?1) treatment attained a weight of 93.2 g. Growth of the fish among the treatments was observed to be improved by the addition of either variety of lupin meal. In contrast, growth of fish fed the soybean meal was equivalent to that of the 0 g kg^?1 fish meal reference, but was poorer at the 400 g kg^?1 inclusion level. Feed intake with the lupin meals was marginally improved with lupin inclusion, but at the higher soybean meal inclusions, feed intake was reduced relative to the fish meal reference diet. The inclusion of the different grains also had significant effects on the physical properties of the pellets.     

The influence of dehulling efficiency on the digestible value of lupin (Lupinus angustifolius) kernel meal when fed to rainbow trout (Oncorhynchus mykiss)

A single batch of Lupinus angustifolius seed was processed to produce a seed meal and dehulled to produce a pure kernel meal. A series of blends were prepared from the seed and kernel meals. The digestible values of these pure and a series of blended meals were compared when fed to rainbow trout using the diet‐substitution method (700 g kg⁻¹ reference: 300 g kg⁻¹ test ingredient). Improvements were observed for each of dry matter, energy and crude protein digestibilities with increasing dehulling efficiency. The relationship between dry matter digestibility and kernel meal proportion was linear and is described by the equation: y = 0.2147x + 40.929. Dry matter digestibility for the 100% kernel meal was 59.8%. The relationship between crude protein digestibility and kernel meal proportion was curvilinear and is described by the equation: y = −0.0019x² + 0.3948x + 81.9143. Crude protein digestibility for the 100% kernel meal was 102%. The relationship between energy digestibility and kernel meal proportion was linear and is described by the equation: y = 0.158x + 48.77. Energy digestibility for the 100% kernel meal was 65.1%. The findings of this study demonstrate that there are significant benefits from using kernel meals over seed meals.     

The effect of dietary n-3 and n-6 fatty acid balance on the growth of the prawn Penaeus monodon

A post-hoc study of the influence of dietary fatty acids of the n-3 and n-6 series on the growth of the prawn, Penaeus monodon showed a clear example of interaction by these nutrients to influence growth. Data from three independent growth studies examining the dietary requirements for linoleic (LOA, 18:2n-6), linolenic (LNA, 18:3n-3), arachidonic (ARA, 20:4n-6), eicosapentaenoic (EPA, 20:5n-2) and docosahexaenoic (DHA, 22:6n-3) acids were standardized through a common reference to allow comparison. Analysis of the variation within the experiments was able to define effects attributable to the individual experiments or the overall dietary n-3 and n-6 levels. A generalized additive model (GAM) indicated that both parameters (experiment, and n-3 and n-6 levels) had significant ( P  < 0.05) effects on growth. Loess nonparametric modelling of the data clearly demonstrates `the effect of relationship' on prawn growth to the levels of dietary n-3 and n-6 fatty acids. The response surface model shows clear effects of both n-3 and n-6, and that the effect of n-3 changes with the level of n-6 (and vice versa). Parametric examination of the relationship ( y =–37.149 x ³ + 160.84 x ² – 118.64 x  + 290.6, r ²=0.492, P  < 0.05) between growth and the ratio between the two fatty acid classes suggested that the optimal ratio of n-3 and n-6 fatty acid is about 2.5 to 1. The results of this study demonstrated that the interaction of the dietary n-3 and n-6 fatty acid classes is an important factor of prawn fatty acid nutrition.     

A factorial growth and feed utilization model for barramundi, Lates calcarifer based on Australian production conditions

To optimize feeds and feed management for barramundi ( Lates calcarifer ), an improved factorial model is required. A growth function describing weight gain by barramundi as a function of fish weight and water temperature was derived from farm and laboratory data. The function was of the form: A maintenance energy demand function was also derived on a similar form and two functions combined to form the basis of a factorial model for this species. An assessment of protein and energy utilization efficiency was undertaken to examine the effect of fish size on the estimation of these parameters. Fish size had a significant effect on energy utilization efficiency on a linear basis, but no such difference was observed if the data were considered using non-linear methods. Protein utilization efficiency was also observed to be clearly non-linear, and although protein deposition capacity differed with fish size, the efficiencies of protein utilization were not affected. Using this factorial model, optimal iterative feed specifications were defined for a range of fish sizes and formulation constraints. A feed demand model was also developed based on the demand for digestible energy.     

Evaluating options for fishmeal replacement in diets for juvenile barramundi (Lates calcarifer)

Two experiments were conducted to examine critical thresholds to fishmeal inclusion in diets for barramundi and also the suitability of a range of different raw materials as alternative protein sources for this species. The first experiment used two diets formulated to the same digestible protein and energy specifications, which were then used to create a series of blended experimental diets that varied in fishmeal content from 0 to 770 g kg^?1. An additional diet containing sodium sulfamerazine was used as a negative control. Feed intake was unaffected with diets containing as little as 11% fishmeal, although broken‐line regression suggests that an inclusion of ～150 g kg^?1 fishmeal is a more likely threshold value. In a second experiment, a further series of diets was formulated for juvenile barramundi according to digestible protein and energy specifications predicted by existing bio‐energetic models. Each of the test raw materials was substituted for fishmeal at either 200 or 300 g kg^?1 (dependent on formulation or extrusion limitations), and two additional diets were included to examine two practical formulations. A diet with only fishmeal as the protein source was included as a reference. Each diet was produced using an APV19 twin‐screw extruder and then vacuum infused with the specified fish oil allocation. Each of the diet pellets produced was also characterized for a range of physical parameters. Fish of an initial weight of 70 ± 0.6 g fish^?1 were randomly allocated across 24 tanks with three replicates per treatment. After 6 weeks, average weight gain across all treatments was 73 ± 12.7 g fish^?1 and feed conversion across all treatments averaged 0.94 ± 0.08 g fish^?1. None of the diets using alternative raw materials had poorer growth or feed conversion than the fishmeal‐based reference diet. The inclusion of either the lupin kernel meals or canola meal significantly improved both weight gain and feed conversion compared to the reference diet. The results from this study demonstrate that there is clear potential to replace the fishmeal content of diets for barramundi without loss of fish performance, up to and including diets with as little as 150 g kg^?1 fishmeal inclusion.